As top T is when you can’t hear  the T sound at the end of a word (common in US English): Cat, wait, want.  

The glottal T is what you hear in words like mount\ain, cert\ain, and acquaint\ance. In a word like accountant, there are two stops: account\ant\.

If you want to hear the US pronunciation or these words, please check them on https://youglish.com/pronounce/acquaintance/english/us

What’s the difference between an acquaintance and a colleague? 

An acquaintance is someone you know socially or casually (not close)
She is an acquaintance from yoga class.
I have a few acquaintances at the gym.
We became acquaintances at a party.

Acolleague is someone you know professionally (Can be at your company or just in your field)
She has a great relationship with her colleagues.
We worked with colleagues from different departments.
I have colleagues in Australia and the UK.